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SILVA FENNICA
Sil a Fennica ol. 52 no. 2 a icle id 9938
Ca ego y: esea ch a icle
h ps://doi.o g/10.14214/s .9938
h p://www.sil a ennica. i
Licenced CC BY-SA 4.0
ISSN-L 0037-5330 | ISSN 2242-4075 (Online)
The Finnish Socie y o Fo es Science
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Jy ki Hy önen1, Egbe Beuke  2 and Anneli Vihe ä-Aa nio 3
Clonal a ia ion in basic densi y, mois u e con en and
hea ing alue o wood, ba k and b anches in hyb id
aspen
Hy önen J., Beuke E., Vihe ä-Aa nio A. (2018). Clonal a ia ion in basic densi y, mois u e
con en and hea ing alue o wood, ba k and b anches in hyb id aspen. Sil a Fennica ol. 52 no.
2 a icle id 9938. 15 p. h ps://doi.o g/10.14214/s .9938
Highligh s
• Hyb id aspen clones di e ed in hei mois u e con en , ash con en , basic densi y and hea -
ing alue.
• S em wood had lowe ash con en , basic densi y and e ec i e hea ing alue han s em ba k.
• The e was signi ican e ical a ia ion in wood and ba k along he s em in mois u e con en
and basic densi y.
Abs ac
Hyb id aspen (Populus emula × P. emuloides) is one o he as es g owing ee species in Fin-
land. Du ing he mid-1990s, a b eeding p og amme was s a ed wi h he aim o selec ing clones
ha we e supe io in p oducing pulpwood. Hyb id aspen can also be g own as a sho - o a ion
c op o bioene gy. To s udy clonal a ia ion in wood and ba k p ope ies, se en clones we e
selec ed om a 12-yea -old ield ial loca ed in sou he n Finland. F om each clone, i e ees
we e ha es ed and samples we e aken om s em wood, s em ba k and b anches o de e mine
basic densi y, e ec i e hea ing alue, mois u e and ash con en . Ve ical wi hin- ee a ia ion in
mois u e con en and basic densi y was also s udied. The di e ences be ween clones we e signi i-
can o almos all s udied p ope ies. Fo all s udied p ope ies he e was a signi ican di e ence
be ween wood and ba k. Wood had lowe ash con en (0.5% s. 3.9%), basic densi y (378 kg m–3
s. 450 kg m–3) and e ec i e hea ing alue (18.26 MJ kg–1 s. 19.24 MJ kg–1), bu highe mois-
u e con en (55% s. 49%) han ba k. The alues o b anches we e in e media e. These esul s
sugges ha he p ope ies o hyb id aspen impo an o ene gy use could be imp o ed by clonal
selec ion. Howe e , selec ing clones based on as g ow h only may be challenging since i may
lead o a dec ease in hyb id aspen wood densi y.
Keywo ds hyb id aspen; clonal a ia ion; basic densi y; ash con en ; mois u e con en ; hea ing
alue; wood; ba k; b anches
Add esses 1Na u al Resou ces Ins i u e Finland (Luke), Na u al esou ces, Teknologiaka u 7,
FI-67100 Kokkola, Finland; 2 Na u al Resou ces Ins i u e Finland (Luke), P oduc ion sys ems,
Finlandian ie 18, FI-58450 Punkaha ju, Finland; 3 Na u al Resou ces Ins i u e Finland (Luke),
P oduc ion sys ems, La oka anonkaa i 9, FI-00790 Helsinki, Finland
E-mail [email p o ec ed]
Recei ed 13 Decembe 2017 Re ised 29 Ma ch 2018 Accep ed 5 Ap il 2018
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Sil a Fennica ol. 52 no. 2 a icle id 9938 · Hy önen e al. · Clonal a ia ion in basic densi y, mois u e con en …
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1 In oduc ion
Hyb id aspen (Populus × we s einii Häme -Ah i), a c oss be ween he na i e Eu opean aspen
(P. emula L.) and Ame ican aspen (P. emuloides Michx.), is conside ed o be he as es g owing
ee species in Finland (Hynynen 1999; Beuke e al. 2016). In he 1950s and 60s, hyb id aspen was
cul i a ed in Finland wi h he pu pose o g owing aw ma e ial o he ma ch indus y, bu wi h he
all o ma ch indus y in he ea ly 1970s in e es in aspen dec eased (Beuke 2000; Kä ki 2001). A
new b eeding p og amme wi h hyb id aspen was s a ed in Finland du ing he mid-1990s wi h he
aim o p oducing pulpwood (Beuke 2000). Indi idual hyb id aspen ees, supe io in g ow h and
quali y, we e selec ed pheno ypically om s ands and ials ha had been plan ed du ing he 1950s
and 60s. The selec ed ees we e ege a i ely p opaga ed h ough mic o-p opaga ion. Because o
he la ge a ia ion be ween he ees in succeeding in he p opaga ion p ocess, only clones ha had
a high a e o p opaga ion success we e selec ed o u he es ing in ield ials.
Fo pulpwood p oduc ion, he ecommenda ion is o plan abou 1200 hyb id aspen plan s
pe hec a e and g ow o 20 o 25 yea s wi hou hinning. A e clea cu ing, he nex gene a ion
can be es ablished om oo sucke s, which a e p oduced in abundance om he exis ing oo
sys em (McCa hy and Ry e 2015; Hy önen 2018). Dense, sp ou o igina ed hyb id aspen s ands
could also be g own o bioene gy applying much sho e o a ions han hose ecommended o
pulpwood (Tullus e al. 2012; Hy önen 2018). Ano he op ion would be a combina ion o sho
o a ion cul i a ion o bioene gy o pulpwood, ollowed by selec i e hinning, and p oduc ion o
la ge dimension ees o enee o sawn imbe (McCa hy and Ry e 2015).
Hyb id aspen g ows bes on e ile o es si es and o me ag icul u al land wi h good ae a-
ion and wa e condi ions (Lu e e al. 2017). A he mos sui able si es in Sou he n Finland he
yield o he i s o a ion s ands can be up o 20 m3 ha–1 pe yea in o a ions o a ound 20 yea s
(Beuke e al. 2016). G ow h o he second o a ion is expec ed o be e en be e due o highe s and
densi y and igo ous ini ial g ow h o he coppice due o he exis ing oo sys em. Hyb id aspen
is e y suscep ible o damage by mammal he bi o es. He bi o e damage may no only a ec he
su i al and g ow h a e o he plan a ions, bu also has a majo e ec on s em and wood quali y.
The plan a ions should be enced agains moose and he indi idual ees p o ec ed agains oles
and ha es. Failu es o ea lie hyb id aspen plan a ions we e mainly due o unsui able o igin o he
plan ing ma e ial, unsui able si e condi ions, as well as poo managemen a es ablishmen phase
and seedling s age o damage by b owsing mammals (Vihe ä-Aa nio 1999).
The p ope ies o he biomass eeds ock can be de e mined by a ious cha ac e is ics,
depending on he end use. Wood densi y is conside ed o be one o he mos impo an quali y
ai s o he use ulness o imbe , as a high densi y has a posi i e e ec on mos o he mechanical
s eng h p ope ies (He äjä i 2004a,b). Na i e Eu opean aspen is known o ha e se e al a ou able
p ope ies ega ding mechanical p ocessing (Söy ilä 1992; He äjä i e al. 2006), bu s udies on
he co esponding p ope ies o hyb id aspen a e limi ed (He äjä i e al. 2006; He äjä i 2009).
Ene gy yield, measu ed as hea ing alue, is one o he mos impo an wood quali y cha ac e is ics
o ene gy plan a ions (Kenney e al. 1990). The ash con en o biomass is known o a y be ween
ee species and ee componen s (Hakkila and Kalaja 1983; Voipio and Laakso 1992; Hy önen
and Nu mi 2015). High wood densi y en ails a highe hea ing alue pe olume, whe eas high
ash con en dec eases he hea ing alue o biomass (Sheng and Aze edo 2005). In addi ion, high
amoun s o ash can also a ec he clogging o he ash handling mechanisms o powe plan s and
may lead o highe cleaning and main enance equi emen s o he boile s (Niu e al. 2016).
In o de o know i wood quali y ai s can be imp o ed h ough he b eeding and selec ion
o supe io hyb id aspen clones, mo e knowledge is needed abou he gene ic a ia ion as well as
he wi hin- ee a ia ion o hose ai s.
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The main objec i e o his s udy was o de e mine he clonal a ia ion o ash and mois u e
con en , basic densi y and hea ing alue among se en selec ed hyb id aspen clones g owing on
o me ag icul u al land in sou he n Finland. In addi ion, we examined he a ia ion o hose ai s
wi hin he ees be ween wood, ba k and b anches, as well as he e ical a ia ion o wood and
ba k.
2 Ma e ial and me hods
2.1 Field ial and clones
The ma e ial o his s udy was ob ained om a hyb id aspen clonal ial in U jala, sou he n Finland
(61°00´N, 23°29´E) ha was es ablished in sp ing 1998. The ial included 25 mic o p opaga ed
hyb id aspen clones. The clones o igina ed om ees ha had been selec ed pheno ypically om
s ands and ials ha we e es ablished in sou he n and cen al Finland du ing he 1950s and 1960s.
The selec ed ees we e supe io in g ow h, had good s em quali y (s aigh wi h ew b anches) and
showed no signs o diseases. The one-yea -old con aine ized hyb id aspen plan s we e g own in he
Haapas ensy jä nu se y o he Fo es Resea ch Ins i u e. The expe imen al layou was a andomized
comple e block design wi h i e eplica es and en ees pe plo ( wo ows o i e ees pe clone
pe plo wi h a spacing o 2 m (wi hin ows) × 4 m (be ween ows)). The ial was es ablished on a
o me ag icul u al ield wi h a sandy clay soil. Be o e plan ing, he soil was p epa ed by plough-
ing. No weed con ol was ca ied ou be o e o a e plan ing. The si e was enced agains moose
and each indi idual ee was p o ec ed agains oles and ha es by a 50 cm high Tubex ube.
Fo his s udy, se en hyb id aspen clones we e selec ed by pheno ype (Table 1). The selec ed
clones we e amongs he en bes clones o heigh g ow h in he ial. Howe e , because in his
s udy he o al ee biomass was s udied, in addi ion o g ow h he clones we e also selec ed o be
di e en in b anching in ensi y, based on ex e io obse a ion. The sha e o b anches om o al
mass in he clones o hyb id aspen a ied om 30 o 43%, he mean being 34%.
Table 1. The hyb id aspen clones included in he s udy, he loca ion o he s and hey we e selec ed om and he o igin
o hei pa en s, as accu a ely as could be eco e ed om he old documen s.
Clone Loca ion o
selec ion
La i ude Longi ude Mo he
species
O igin o he
mo he
Fa he
species
O igin o he
a he
7Vih i 60°20´ 24°26´ Populus
emula
Tuusula,
Finland
Populus
emuloides
Aleza Lake,
Ca iboo, BC, Canada
14 Lapinjä i 60°37´ 26°11´ Populus
emula
Toi akka,
Finland
Populus
emuloides
Maple, On a io,
Canada
20 Nu mijä i 60°30´ 24°42´ Populus
emuloides
Aleza Lake,
Ca iboo, BC, Canada
Populus
emula Finland
21 Vih i 60°20´ 24°26´ Populus
emula
Helsinki,
Finland
Populus
emuloides
Gal , On a io,
Canada
24 Vaajakoski 62°15´ 25°54´ Populus
emula
Tuusula,
Finland
Populus
emuloides
Maple, On a io,
Canada
26 Vaajakoski 62°15´ 25°54´ Populus
emuloides
Go henbu g bo anical
ga den, Sweden
Populus
emula
Tuusula,
Finland
27 Loppi 60°37´ 24°27´ Populus
emula
Punkaha ju,
Finland
Populus
emuloides Canada
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2.2 Field measu emen s and sample collec ion
One ee pe clone was selec ed a andom om each block ( o al i e ees/clone) and ha es ed
du ing win e (Decembe –Janua y) a e 12 g owing seasons. Howe e , due o mo ali y, wo ees
o clone 21 had o be aken om block 1 and wo ees o clone 27 om blocks 1 and 4. A e
elling, heigh (dm) and diame e a b eas heigh (DBH, cm) o each ee we e measu ed. The
ees we e delimbed and he b anches o each ee we e collec ed, weighed and bundled. A sample
consis ing o 10 cm sec ions om op, middle and base sec ions o each b anch bundle was aken
o analysis. F om he s em, 5 o 6-cm- hick sample discs we e sawn a a heigh o 0.6 m, 1.3 m
and 2 m om he s ump and om he e on e e y wo me es o he op o each ee. Only wo ees
we e all enough o be sampled a 12 me es heigh . Because he e we e only wo 12 m samples
hey we e excluded om he da a. All samples we e ma ked ( ee numbe , sampling heigh ) and
packed in plas ic bags.
2.3 Assessmen o ash and mois u e con en , basic densi y and hea ing alue
In he labo a o y, he diame e wi h and wi hou ba k o each disc was measu ed in wo di ec ions
pe pendicula ly. Subsequen ly, he s em sample discs we e di ided ho izon ally in o wo discs
(2.5–3 cm in hickness). O hese, one disc was used o de e mining basic densi y using he wa e
eplacemen me hod (Olesen 1971). A e measu ing he o al olume wi h ba k o hese discs,
hey we e deba ked (ou e and inne ba k) and e-measu ed o ob ain he olume o wood. The
olume o ba k was calcula ed on he basis o hese wo measu emen s. Then, he ba k and wood
samples we e d ied a +105 °C o cons an weigh and weighed, and mois u e con en and basic
densi y calcula ed sepa a ely o wood and ba k. One basic densi y measu emen o ba k was
omi ed om he analysis due o a measu emen e o .
The o he disc hal es, as well as he b anch sample, we e used o analysing he ash con en
and hea ing alue o wood, ba k and b anches. These sample discs we e deba ked ca e ully. Then
he wood and ba k samples om all disks belonging o one and he same ee we e uni ed o o m
one wood and one ba k sample pe ee, d ied a +70 °C o cons an weigh and milled.
Calo i ic hea ing alue (qp(g oss)) was de e mined wi h an IKA C 500 calo ime e . In o de
o calcula e he e ec i e (qp(ne )), lowe , ne calo i ic alue on a d y basis) hea ing alue i is
necessa y o known he hyd ogen con en o he compa men s, since he hea o condensa ion o
wa e apou c ea ed du ing combus ion has o be aken in o accoun . The hyd ogen concen a ions
used we e ob ained om Nu mi (1997) and o b anches and ba k hey we e calcula ed as means
om igu es p esen ing alues o di e en sized b anches and inne and ou e ba k (s em 6.32%,
b anches 6.07%, ba k 6.23%). The ollowing o mula was used in he calcula ion (see Alakangas
e al. 2016):
qp(ne ) = qp(g oss) – 212.2 × w(H)d – 0.8 × [w(O)d + w(N)d]
qp(ne ) = ne calo i ic alue on a d y basis a cons an p essu e, kJ kg–1
qp(g oss) = g oss (e ec i e) calo i ic alue on a d y basis, kJ kg–1
w(H)d = hyd ogen con en in d y bio uel, %
w(O)d = oxygen con en in d y uel, %
w(N)d = ni ogen con en in d y uel, %
Fo w(O)d + w(N)d de aul alue o 41% was used (Alakangas e al. 2016). Ash con en o
he samples was de e mined by ashing he samples a 550 °C o 8 hou s.
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2.4 S a is ical analyses
The basic densi y and mois u e con en o s em wood, s em ba k and he whole s em (wood plus
ba k) o each ee was calcula ed as a mean weighed by diame e squa ed a each measu emen
poin a di e en heigh s. The clonal di e ences in he wood, ba k and s em basic densi y, mois u e
con en , hea ing alue and ash con en we e es ed wi h mixed linea models wi h he clone as ixed
e ec , eplica ion as andom e ec and ee heigh as co a ia e. The clonal means we e compa ed
using S uden ’s LSD es a signi icance le el p < 0.05. The e ec o clone and sampling heigh
on basic densi y and mois u e con en o wood, ba k and s em was es ed wi h epea ed measu es
analysis o a iance, whe e sampling heigh was used as a wi hin-subjec a iable. Due o se e al
ees being sho e han 10 m, he analysis was con ined o 8 m o heigh . When in he epea ed
ANOVA models Mauchly’s es indica ed ha he assump ion o sphe ici y had been iola ed, he
deg ees o eedom we e co ec ed using G eenhouse-Geisse es ima es o sphe ici y. When es -
ing igu es in pe cen age e ms, a iance s abilizing ans o ma ions o squa e oo a csine was
used. The pai wise linea dependences be ween he s udied ai s we e examined wi h Pea son’s
linea co ela ion coe icien s calcula ed on he clonal means. All analyses we e done using he
IBM SPSS 22.0 p og amme.
3 Resul s
3.1 T ee heigh and diame e
The mean heigh o all ees was 10.6 m and hei DBH 10.8 cm (Fig. 1). The e we e signi ican
di e ences in he heigh o he clones, bu no in hei DBH.
3.2 P opo ion o wood and ba k
The clones di e ed in wood (and ba k) ac ion in he s ems (Fig. 2). The amoun o wood in he
hyb id aspen s ems was on a e age 84.9%, wi h a ange o 8 pe cen age poin s be ween clones.
The wood ac ion o he s em biomass emained qui e cons an un il up o 6 m heigh a e which
i s a ed o dec ease (Fig. 2). The dec ease o he wood ac ion owa ds he op o he ee was
signi ican . The e was also a signi ican sampling heigh × clone in e ac ion o he ac ion o s em
Fig. 1. Mean heigh (A) and DBH (B) o he s udied hyb id aspen
clones. Ba s indica e s anda d e o . Clones ma ked wi h he same le -
e s do no di e om each o he a he 0.05 signi icance le el.

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wood. Fo clonal means he e was a s ong posi i e co ela ion ( = 0.883, p = 0.008) be ween ee
heigh and he p opo ion o wood in he s ems.
3.3 Ash con en
The ash con en was lowes in hyb id aspen wood wi h a mean alue o all clones o 0.45%. The e
we e clonal di e ences in ash con en o he wood (Fig. 3). Clone 21 had he lowes ash con en
(0.40%) and clone 26 he highes (0.49%). Ash con en o he ba k was almos 10 imes highe
han ha o he wood (mean o all clones 3.9%). Clone 20 had excep ionally low ash con en in
he ba k compa ed o o he clones (Fig. 3). The ash con en o he b anches (mean o all clones
2.4%) was in e media e o ha o he wood and ba k. Ash con en o he wood and ba k did no
co ela e signi ican ly wi h he size o he ees (DBH, H). Howe e , because he ash con en o
he ba k was much highe han ha o he wood, he ash con en o b anches co ela ed nega i ely
wi h DBH ( = –0.475, p = 0.004) and H ( = –0.358, p = 0.035). Bigge ees had bigge b anches and
hus ela i ely less ash ich ba k in he b anches. When calcula ed on clonal means, no signi ican
co ela ion was ound be ween he ash con en o wood and ash con en o ba k.
Fig. 3. The mean ash con en o wood (A), ba k (B) and b anches (C) in hyb id aspen clones. Lines inside ba s indica e
s anda d e o . T ee heigh was used as a co a ia e. Clones ma ked wi h he same le e s do no di e om each o he
a he 0.05 signi icance le el.
Fig. 2. The mean wood ac ion o he o al s em biomass (A) and he wood
ac ions o s em biomass a di e en sample heigh s (B) in he s udied hyb id
aspen clones. T ee heigh was used as co a ia e. Clones ma ked wi h he same
le e s do no di e om each o he a he 0.05 signi icance le el.
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3.4 Mois u e con en
The mois u e con en o he hyb id aspen clones was highes in he wood (on a e age 54.9%),
lowes in he ba k (48.9%) and in e media e in he b anches (50.1%) (Fig. 4). The a e age mois u e
con en o he whole s em wi hou b anches (54.3%) was only sligh ly lowe han ha o he wood
ac ion due o he small sha e o ba k o he o al s em biomass. The e we e signi ican clonal
di e ences in he mois u e con en o wood, ba k, s em as well as b anches. Fo wood mois u e
con en he co a ia e (heigh ) was signi ican indica ing ha bigge ees had lowe mois u e con-
en . No signi ican co ela ion was ound be ween he mois u e o wood and mois u e o ba k,
when calcula ed on clonal means.
The e ec o sampling heigh on wood, ba k and s em mois u e con en s was signi ican
(Fig. 5). Howe e , wood and ba k mois u e con en s changed di e en ly in he e ical di ec ion.
The mois u e con en o wood was lowes a he base o he s em and inc eased in a e ical di ec-
ion eaching i s maximum a 2–4 m heigh , hen g adually dec easing u he upwa ds and in mos
o he clones eaching i s minimum a op o he ees (Fig. 5). The ba k mois u e con en was
lowes a he base o he s em and inc eased consis en ly owa ds he op o he ee. The mois u e
o s em (wood and ba k) was lowes a he s em base. Howe e , e ical changes in s em mois u e
we e smalle han hose obse ed in wood and ba k since he mois u e o he wood was low and
ha o ba k high a he op o he s ems. The e we e signi ican clonal di e ences in he mois u e
con en o he wood, ba k and s em. The clone × sampling heigh in e ac ion was signi ican o
wood and s em mois u e con en indica ing ha he s udied clones had di e en mois u e con en
a di e en heigh s.
Fig.4. The mean mois u e con en o wood (A), ba k (B), s em (wood and ba k)
(C) and b anches (D) o he s udied hyb id aspen clones. T ee heigh was used
as co a ia e. Clones ma ked wi h he same le e s do no di e om each o he
a he 0.05 signi icance le el.
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3.5 Basic densi y
The a e age basic densi y o wood o all clones was 378 kg m–3 and ha o ba k 450 kg m–3. The e
we e signi ican clonal di e ences in basic densi y bo h o wood and ba k (Fig. 6). The di e ence
be ween he clones wi h he highes and lowes basic densi y o wood and ba k was 44 kg m–3
and 91 kg m–3, espec i ely. Co ela ion be ween he densi y o wood and densi y o ba k was no
signi ican , when calcula ed on he clonal means. Fo clonal means he e was, howe e , a s ong
nega i e co ela ion be ween ee heigh and densi y o wood ( = –0.796, p = 0.032), as well as
be ween heigh and densi y o s em ( = –0.832, p = 0.020).
The e ec o sampling heigh on wood, ba k and s em basic densi y was signi ican (Fig. 7).
The basic densi y o hyb id aspen clones dec eased om he base o he s em up o 4–6 m heigh ,
bu inc eased again u he upwa ds owa d he op o he ee (Fig. 7). The clonal a ia ion was
signi ican as was he clone × sampling heigh in e ac ion. Clone 24 had a he lowe pa s o he
s em excep ionally low basic densi y (Fig. 7). The a ia ion in basic densi y o ba k was highe
han ha o wood. Basic densi y o ba k was highes close o he g ound and gene ally dec eased
up o 4 m, sligh ly inc easing again owa ds he op o he ees.
Fig. 5. The mean mois u e con en o wood (A), ba k (B), and s em (wood and ba k) (C) o he s udied hyb id aspen
clones a di e en sampling heigh s.
Fig. 6. The mean basic densi y o wood (A), ba k (B) and s em (wood and ba k) (C) o he s udied hyb id aspen clones.
S anda d e o o he mean. T ee heigh was used as co a ia e. Clones ma ked wi h he same le e s do no di e om
each o he a he 0.05 signi icance le el.
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3.6 Hea ing alue
Analysis o co a iance showed clonal di e ences in he e ec i e hea ing alue o bo h s em
wood and s em ba k o hyb id aspen clones (Fig. 8). Fo wood, also he co a ia e ( ee heigh )
was signi ican . Howe e , he e we e no signi ican di e ences in he e ec i e hea ing alue o
he b anches o he di e en clones. The e ec i e hea ing alue o wood was lowe han ha o
ba k, and ha o b anches was in e media e. The a e age e ec i e hea ing alue o wood was
18.264 MJ kg–1, ba k 19.239 MJ kg–1 and ha o b anches 18.747 MJ kg–1. The di e ence in hea -
Fig. 7. Mean basic densi y o wood (A), ba k (B), and s em (wood and ba k) (C) o he s udied hyb id aspen clones a
di e en sampling heigh s.
Fig. 8. The mean e ec i e hea ing alue o o en d y biomass o wood (A), ba k
(B), b anches (C) and s em (wood and ba k) (D) o hyb id aspen clones. T ee
heigh was used as co a ia e.